The 14 cases all involve men who visited areas with Zika outbreaks, and who may have infected their female sex partners, who had not traveled to those areas.
Zika virus is mainly spread by mosquito bites, and sexual transmission has been considered rare. There have been two reported cases, including a recent one in Texas, and at least two other reports of the Zika virus found in semen.
Mosquito-borne Zika outbreaks have erupted across most of Latin America and the Caribbean in the last year. So far, all the 82 Zika infections diagnosed in the U.S. have involved people who traveled to outbreak regions.
On Tuesday, the Centers for Disease Control and Prevention said the 14 possible cases of sexual transmission in the U.S. include two women whose infections have been confirmed. Tests have not been completed for their male partners.
In four other cases, preliminary tests indicate women were infected but confirmatory tests are pending. Eight other cases are still being investigated, according to a CDC statement.
Several of the 14 are pregnant, but the CDC refused to be more specific.
The agency said there's no evidence that women can spread the virus to their sex partners, but more research is needed.
In most people, Zika causes mild or no symptoms - fever, joint pain, rash and red eyes - that last about a week. But in Brazil, health officials are investigating a possible connection between the virus and babies born with brain defects and abnormally small heads.